The present invention is directed to a system and method for cutting hearing aid shells using an ellipsoidal line cut methodology.
Hearing aid shells that house various hearing aid components are designed to fit into the ear of a wearer. However, each user's ear is shaped differently so that a one-size-fits all approach cannot be used or would result in a poor fit and cause discomfort for the wearer. For this reason, customized shells are created that correspond to the particular shape of the user's ear.
In order to create such a customized shell, an impression of the user's ear is taken using a soft moldable material that conforms to the shape of the user's ear which subsequently hardens. This impression can then be used to create a hearing aid shell design that precisely matches the user's ear, resulting in a good fit and comfort for the wearer.
Traditionally, this process would involve a manual creation, cutting, and trimming of the shell, based on the impression. However, advances in the field have permitted the use of computer software to assist in the creation of shell designs. This software works from a digitized model of the impression and can create a digitized model of the shell from this impression that can be operated on with the use of a computer program and/or can assist in automated procedures for modifying the shelf.
FIG. 1A illustrates a typical digitized model of a hearing aid shell 10 to which a bottom cut plane 50 (FIG. 2) has been applied, creating a bottom cut contour 52.
FIG. 2 illustrates known application of the Bottom Cut Plane 50 to the hearing aid shell 10. A hearing aid shell 10 has a Bottom Cut Plane 50, which defines the border of the bottom opening of the shell 10. After a scanning/triangulation of the shell 10, which creates a 3D digital definition of a shell shape, the shell 10 typically has a non-planar contour which defines the Bottom of the Shell. In order to make the contour planar, the Bottom Cut Plane 50 is introduced which defines a new topology of the shell opening contour (Bottom Cut Plane Contour) 52, which is defined as the intersection between the shell 10 and the Bottom Cut Plane 50. The remove portion 14, i.e., the material below the plane 50, is removed and all holes between the plane 50 and the keep portion 12 of the remaining shell are filled with material.
One of the basic detailing and modeling procedures is to utilize what is know as a line cut plane that is used to define a cut plane for detailing operations, separating the shell 10 along a planar boundary into a keep portion 12 and a remove portion 14, producing a Line Cut Plane contour 62. The face that is created by the cut plane must be filled in order to create a coherent shell. Theoretically, filling could be performed by simply applying the plane as an actual part of the shell. In the real world, this would create sharp edges and unpleasant aesthetics that are not practical. Therefore, various techniques have been applied to adapt the surface 64 created by the line cut plane into a more practical shape.
FIG. 1C illustrates the application of a rounding process where the cutting area defined by the cut plane has been filled and rounded according to certain defined parameters. A modification of this technique can be to provide the rounding function that includes an offset plane which provides boundaries to the rounding operation (see FIG. 1E).
FIG. 1D illustrates the application of an alternate tapering process, which serves to remove a tip area of the shell with a smoothing bounding area, such that after the cut plane is applied and filled, a smoothing operation is performed. Prahl Tapering is a refinement of the tapering that utilizes an offset plane to further define a rounding effect. Similarly, Helix Tapering is used to reshape the helix material of the shell with a rounding effect, according to various parameters. A “Prahl Taper” refers to a polynomial shrink of the canal of the shell impression usually initiated from the aperture to the canal tip. It is characterized by an erosion parameter, which is the measure of the required shrink and a maximum reduction parameter, which determines the required reduction in canal length. A “Helix Taper” refers to a polynomial shrink of the helix which begins at the highest point on the helix to a user defined position of the helix.
These shaping procedures generally replicate the manual procedures that have been used to craft the shells in the past to change the shape of a part of the shell where the button/bottom cut plane is involved. In essence, they replicate cutting with a knife and then performing some rounding around the cut. The most classic use examples are for, e.g., decreasing the full impression to fit the size of a half-shell or mini-canal design, or, for example, cutting off the intertragal notch. In these examples, some material is removed from the shell and the nature of removing the material requires that bottom cut contour is changed, or actually shrunken. These current approaches of rounding and tapering create a relatively aesthetically unpleasant resultant shell.